This invention relates to radiation cure reactors. More specifically, this invention relates to a radiation cure reactor having apparatus for cooling the reactor and a radiation curable product, coating, ink, or the like subjected to radiation within the reactor. The invention is applicable to a wide variety of radiation curable products, items and materials.
A wide variety of coatings and the like are applied to the surfaces of various substrates. For example, various plastic or vinyl films, resinous-based finishes, and the like are applied to substrates such as particle board, etc. Moreover, various inks are used for printing on papers of many different types and test strengths. In industrial processes, it is highly desirable to cure these coatings and inks as quickly as possible so that subsequent product processing steps may occur. It is equally important that the coating or ink be cured in an efficient, inexpensive manner which does not detrimentally affect the desired quality of the finished product.
In the prior art, it has been common practice to use conventional hot air or infrared ovens for curing industrial coatings and inks. With such ovens, the coated substrate is conveyed through the oven where it is subjected to elevated temperatures for drying and curing of the coating or ink. It is well known, however, that hot air or infrared ovens are unsatisfactory for curing many types of industrial products since the heat generated by the ovens can cause the products or surface coating to warp, distort, or shrink. This is particularly true with plastic or vinyl based surface films, and with many types of paper when printed. Distortion of the product or of the surface coating on the product makes the finished item unacceptable for sale or use. Moreover, it has been found that hot air or infrared ovens require prolonged curing times, and tend to use excessive quantities of energy.
Radiation cure reactors have been proposed in an effort to overcome the disadvantages of hot air ovens. Radiation cure reactors include a source of radiation such as an ultraviolet radiation producting lamp carried in a relatively closed chamber which confines and directs radiation onto the surface of a substrate. Theoretically, radiation cure equipment quickly and completely cures radiation curable coatings and products without requiring the presence of heat. However, modern commercially available radiation lamps operate at high temperatures, in the area of about 1100.degree. F., and thereby produce large quantities of heat during operation. Accordingly, modern radiation cure reactors experience a significant heat build-up within the closed lamp chamber which tends to adversely affect the coating or the product being cured. Moreover, modern ultraviolet radiation lamps tend to produce undesirably large quantities of infrared radiation during operation to expose the surface of the substrate being cured to an instantaneous temperature substantially higher than the air temperature within the reactor as the substrate passes in close proximity with a radiation producing lamp. The result is that radiation cure reactors sometimes expose the substrate to higher temperatures than those encountered with the more conventional hot air ovens.
Some attempts have been made in the prior art to reduce the heating effects of modern radiation cure equipment. One such attempt comprises supplying fan-forced ambient air through a duct network and directly onto the surface of the irradiated substrate. Another system comprises high volume, fan-forced circulation of ambient air freely throughout the relatively closed lamp chamber. In both systems, the steady state temperature of air within the chamber is reduced, but neither system avoids the substantially instantaneous exposure of the substrate to extremely high temperature resulting from infrated components of radiation as the substrate passes in close proximity with the radiation producing lamp.
Other attempts have been made in the prior art to control the surface temperature of a substrate during curing by means of coolant-carrying tubing within the enclosed lamp chamber. See, for example, copending U.S. Patent Application Ser. No. 742,580, owned by the assignee of this invention. The tubing is positioned in close proximity with the substrate and the radiation producing lamps so as to absorb heat without blocking the field of radiation. Again, this system results in a lower steady state air temperature within the enclosed lamp chamber, but it does not protect against instantaneous excessive temperatures resulting from direct radiation from the lamps.
The radiation cure reactor of this invention overcomes the problems and the disadvantages of the prior art by providing an improved cooling system for controlling excessive substrate surface temperatures during curing.